The most common elements vary dramatically depending on where you look. Hydrogen and helium dominate the universe by an enormous margin, together making up roughly 98 percent of all ordinary matter. On Earth, the picture shifts: iron and oxygen are the heavyweights, while the oceans are defined by dissolved sodium and chloride, and living things run almost entirely on just six elements. Understanding which elements show up where, and why, turns out to be a story that stretches from the first minutes after the Big Bang to the soil beneath your feet.
Where the Lightest Elements Came From
Hydrogen, helium, and trace amounts of lithium were the first elements to exist. They were forged in the first few minutes of the universe during a process called Big Bang nucleosynthesis, when temperatures were on the order of a billion degrees and conditions were dense enough for nuclear reactions to occur.1Physica Scripta. Review of Big Bang Nucleosynthesis and Primordial Abundances Almost all the helium you encounter today, whether in a party balloon or leaking from a natural gas well, traces its origin to that brief window of cosmic creation. The existence of a universal primordial helium abundance is one of the strongest pieces of evidence that the early universe went through a hot, dense phase.2Physics Reports. Helium and Big Bang nucleosynthesis
Hydrogen remains the most abundant element in the cosmos by far. Stars are mostly hydrogen, and they spend most of their lives fusing it into helium. That reaction powers our sun and every other main-sequence star. Helium is the second most abundant element overall, though on Earth it is comparatively scarce because it is too light for our planet’s gravity to hold onto permanently. Most terrestrial helium is actually a byproduct of radioactive decay deep underground, trapped in rock formations alongside natural gas.
How Stars and Collisions Built Everything Heavier
Elements heavier than helium were not made in the Big Bang. They required stars. Inside stellar cores, nuclear fusion progressively builds heavier nuclei: hydrogen becomes helium, helium becomes carbon and oxygen, and in massive stars the chain continues through neon, silicon, and eventually iron. Iron is a dead end for fusion because fusing it absorbs energy rather than releasing it. When a massive star runs out of fuel, it collapses and explodes as a supernova, scattering these elements into space.
But what about elements heavier than iron, like gold, platinum, and uranium? For decades, the origin of these elements was an open puzzle. A leading hypothesis pointed to the rapid neutron capture process, or r-process, which requires an environment flooded with free neutrons. The first direct detection of a neutron star merger through both gravitational waves and electromagnetic signals confirmed that these violent collisions are a major production site for heavy elements.3Astronomy & Astrophysics. The first direct double neutron star merger detection: Implications for cosmic nucleosynthesis Follow-up observations with the James Webb Space Telescope have since identified signatures of heavy neutron-capture elements in the afterglow of compact object mergers, reinforcing the connection.4Nature. JWST detection of heavy neutron capture elements in a compact object merger Current evidence suggests that neutron star mergers are not just a contributor but likely the dominant source of r-process elements in the universe. The gold in your jewelry and the uranium in nuclear fuel rods were, in all likelihood, forged when two neutron stars spiraled into each other billions of years ago.
Elements Inside the Earth
Earth’s bulk composition is dominated by iron, oxygen, silicon, and magnesium. How these elements are distributed through the planet’s layers depends on their chemical affinities, a concept first mapped out by the geochemist Victor Goldschmidt in 1923. Goldschmidt classified elements based on whether they preferentially dissolve into metallic phases, sulfide phases, or silicate phases during planetary differentiation. He drew evidence from the distribution of elements in different meteorite phases and from metallurgical experiments measuring how elements partition among coexisting metal, sulfide, and silicate slag.5American Mineralogist. Goldschmidt’s geochemical classification of the elements: The evolution of a nuanced hypothesis
The practical upshot is straightforward. Iron-loving elements like iron, nickel, cobalt, and platinum-group metals sank into Earth’s metallic core during the planet’s formation, which is why these materials are relatively rare at the surface compared to their cosmic abundance. Silicate-loving elements like silicon, aluminum, calcium, and the alkali metals concentrated in the mantle and crust. That is why the rocks you walk on are rich in silicon and aluminum but poor in platinum. Sulfur-loving elements like copper, zinc, and lead tend to concentrate in sulfide mineral deposits, which is exactly where miners go looking for them.
Earth’s crust, the thin outer shell we interact with, is overwhelmingly oxygen (by weight, about 46 percent) and silicon (about 28 percent), followed by aluminum, iron, calcium, sodium, magnesium, and potassium. These eight elements account for the vast majority of crustal rock. Everything else, including metals we consider common in daily life like copper and zinc, is present at concentrations measured in tens of parts per million.
What the Oceans Are Made Of
Seawater is not just salty; it has a remarkably consistent chemical recipe everywhere on Earth. The major dissolved ions are chloride, sodium, sulfate, magnesium, calcium, and potassium. As far back as the 1860s, chemists recognized that the ratios of these major salts in seawater from different locations are almost constant, a principle that still holds today and underpins how oceanographers define salinity.6Elsevier. The composition of Standard Seawater and the definition of-the Reference-Composition Salinity Scale This constancy exists because the oceans are so well mixed over geological time that local variations get smoothed out.
Beyond the major ions, seawater contains traces of nearly every naturally occurring element. Some of these trace elements, like dissolved iron, are biologically critical. Iron limits the growth of photosynthetic plankton across vast stretches of the open ocean, even though it is one of the most abundant elements on Earth overall. The reason is that iron is extremely insoluble in oxygenated seawater, so its dissolved concentration stays vanishingly low. Other trace elements in seawater, like uranium and lithium, have attracted industrial interest. The oceans contain an estimated four billion tons of dissolved uranium, for instance, though extracting it cost-effectively remains an unsolved engineering problem.
The Atmosphere and Its Gases
Earth’s atmosphere is roughly 78 percent nitrogen and 21 percent oxygen by volume, with argon making up most of the remaining one percent. These three gases can be separated industrially through cryogenic distillation, which cools air until its components liquefy at different temperatures. Simulations of this process confirm that nitrogen, oxygen, and argon can be obtained at high purity this way.7ACS Omega. Novel Study on Cryogenic Distillation Process and Application by Using CHEMCAD Simulation This is the primary industrial source for all three gases, supplying everything from hospital oxygen to the nitrogen blankets used in food packaging.
Noble gases like neon, argon, krypton, and xenon are all present in the atmosphere at low concentrations. Argon is relatively abundant because it accumulates from the radioactive decay of potassium-40 in rocks, which releases argon-40 that gradually escapes into the air. Studies of gases emanating from fault zones have confirmed that neon, argon, and nitrogen in certain geological settings are atmospheric in origin, carried underground by circulating groundwater and released back at the surface.8Journal of Geophysical Research: Solid Earth. Behavior and origin of helium, neon, argon, and nitrogen from active faults Helium, by contrast, behaves differently: some of it in fault zones is radiogenic, meaning it was produced by radioactive decay underground rather than arriving from the atmosphere.
The Elements of Life
Living organisms use a surprisingly small slice of the periodic table. The bulk of any organism, whether a bacterium, a tree, or a person, is built from just six elements: carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. These are sometimes called the macronutrient elements of life. Beyond those six, a handful of ions including magnesium, potassium, sodium, and calcium play essential roles in cell function, nerve signaling, and structural support.9PubMed Central. The elements of life: A biocentric tour of the periodic table
Carbon’s dominance in biology comes from its unique chemistry: it forms stable bonds with itself and with many other elements, allowing the enormous structural variety needed for proteins, DNA, fats, and sugars. Oxygen and hydrogen are abundant largely because water is the solvent of life. Nitrogen is a key component of amino acids and nucleic acids, phosphorus is central to energy transfer and the backbone of DNA, and sulfur shows up in certain amino acids and enzyme cofactors. These six elements are not rare on Earth, but their biological importance is out of all proportion to their simple availability.
Trace Metals Your Body Depends On
Beyond the big six, your body requires at least ten metals in small quantities for normal functioning. These include four main-group metals (sodium, potassium, magnesium, and calcium) and six transition metals: manganese, iron, cobalt, copper, zinc, and molybdenum. These metals sit at the active centers of enzymes that catalyze reactions your cells could not perform otherwise.10PubMed. Essential metals in health and disease Iron carries oxygen in hemoglobin, zinc supports immune function and wound healing, copper participates in energy production, and cobalt is part of vitamin B12.
The balance matters enormously. Iron and copper are what chemists call redox-active metals, meaning they readily gain or lose electrons. This property makes them useful inside enzymes but dangerous when they escape control, because they can generate highly reactive molecules that damage DNA and cell membranes. A deficiency in any of the essential trace metals leads to specific health problems that can typically be reversed with supplementation.11PubMed. Relevance, essentiality and toxicity of trace elements in human health Iron deficiency is the most widespread nutritional deficiency worldwide, affecting billions of people, while zinc deficiency is especially common in regions where diets rely heavily on grains, which contain compounds that block zinc absorption.
Where these trace metals come from, ultimately, is soil and water. Plants pull them from the ground, animals eat the plants, and the metals cycle through food webs. Phosphorus follows a similar route, and its availability in soil often limits crop growth. In agricultural settings, phosphorus is frequently the bottleneck nutrient, which is why phosphate fertilizers are so widely used.
Rare Earth Elements Are Not Actually Rare
One of the more persistent misconceptions about elements is that “rare earth elements” are genuinely scarce. They are not. The total abundance of rare earth elements in Earth’s crust is about 169 parts per million, and the most common of them, cerium, occurs at roughly 63 parts per million. That puts cerium in the same league as copper (about 60 ppm) and makes it more abundant in the crust than cobalt (about 25 ppm) or lead (about 14 ppm).12Applied Geochemistry. Global rare earth element resources: A concise review
The “rare” in the name is historical and refers to the fact that these elements seldom form concentrated, easily mined deposits. They tend to be dispersed throughout many different minerals rather than pooling into rich veins the way copper or gold sometimes do. Extracting and separating individual rare earth elements from one another is chemically difficult because they share very similar properties. This is what makes them strategically sensitive: not scarcity in the ground, but difficulty in processing and the geographic concentration of current mining operations.
Rare earth elements matter because they are essential to modern technology. Neodymium goes into the powerful permanent magnets used in wind turbines and electric vehicle motors. Europium and terbium provide the red and green phosphors in display screens. Lanthanum is used in rechargeable batteries and camera lenses. As demand for clean energy technologies grows, so does the pressure to diversify where these elements are sourced, with new mining and recycling efforts underway in several countries.
What Meteorites Tell Us About Planetary Ingredients
If you want to know what the solar system was made of before planets formed, the best evidence comes from a particular class of meteorites called carbonaceous chondrites. These are among the oldest and least altered materials in the solar system, and their chemical composition serves as a reference point for estimating how elements were distributed before planets differentiated into cores, mantles, and crusts.13Geochimica et Cosmochimica Acta. The chemical composition of carbonaceous chondrites: Implications for volatile element depletion, complementarity and alteration When geochemists say that Earth is “depleted” or “enriched” in a given element, they often mean relative to these chondrite compositions.
The Moon provides another useful comparison. Analyses combining remote sensing data, lunar samples, and gravity measurements suggest that the Moon and Earth have roughly the same concentrations of refractory elements (those with high melting points, like aluminum and calcium), within about 20 percent.14The Royal Society. Lunar bulk chemical composition: a post-Gravity Recovery and Interior Laboratory reassessment But the Moon is severely depleted in volatile elements, the ones that evaporate easily. Moderately volatile elements like potassium, rubidium, and cesium are depleted by about 75 percent compared to Earth, and highly volatile elements like thallium and cadmium are depleted by roughly 99 percent. This pattern is strong evidence that the Moon formed in an extremely high-energy event, most likely a giant impact, that drove off its volatile inventory.
Why Some Common Elements Are Hard to Get
Abundance in the crust does not automatically translate to easy access. Aluminum is the most abundant metal in Earth’s crust, yet it took until the late 1800s for industrial processes to make it cheap. The reason is chemical: aluminum binds tightly to oxygen in minerals like feldspar and clay, and breaking those bonds requires enormous energy. The Hall-Héroult process, which uses electrolysis of molten aluminum oxide, finally made mass production feasible, but it remains one of the most energy-intensive industrial processes in the world.
Silicon tells a similar story. It is the second most abundant element in the crust, but producing the ultra-pure silicon needed for computer chips requires multiple rounds of chemical refining and crystal growth. The silicon in a beach rock and the silicon in a microprocessor might be the same element, but the path from one to the other is long and expensive.
Conversely, some elements that are genuinely rare in the crust are easy to obtain because they concentrate in specific geological settings. Gold, for example, makes up only about 0.004 parts per million of the crust, but hydrothermal processes can concentrate it into veins thousands of times richer than the background. This is why gold has been mined for millennia while aluminum, vastly more abundant, was once more expensive than gold itself.
Elements at the Edges of the Periodic Table
At the far end of the periodic table sit the synthetic and extremely heavy elements like oganesson (element 118) and tennessine (element 117). These do not occur naturally in any meaningful sense. They are created atom by atom in particle accelerators, exist for fractions of a second before decaying, and serve primarily as tools for understanding nuclear physics. No one will ever find a deposit of oganesson.
Just below these purely synthetic elements are the very heavy natural elements like uranium and thorium. Uranium is found in trace amounts in most rocks and even in seawater, but economically viable deposits are concentrated in certain geological settings, particularly sandstone-hosted roll-front deposits and unconformity-related deposits in places like Canada, Kazakhstan, and Australia. Thorium is about three times more abundant than uranium in the crust and is found in monazite sands, which also happen to be a source of rare earth elements. Both uranium and thorium are radioactive, and their slow decay over billions of years is a major source of the internal heat that drives plate tectonics and volcanism.
Technetium, element 43, holds the distinction of being the lightest element with no stable isotopes. Every atom of technetium on Earth today is either freshly produced in nuclear reactors or generated by the radioactive decay of heavier elements. Despite being “missing” from nature, technetium is widely used in medicine: a particular isotope is the most commonly used radioactive tracer in diagnostic imaging, with tens of millions of medical scans performed with it annually. Its absence from the natural world and its ubiquity in hospitals make it one of the more surprising entries on any list of elements that matter to daily life.